Field of the Invention
The invention relates to a circuit configuration for shutoff of a semiconductor component controlled by field effect, in the event of excess current, including a controllable switch being located between the gate terminal and the cathode terminal and being made conducting by a control signal.
Such a circuit configuration is widely used and has been described for a MOSFET, for instance, in German Patent DE 30 34 927 C2. The controllable switch discharges the gate-to-source capacitance of the semiconductor component when it is made conducting and thus blocks the semiconductor component.
When there is excess current in the semiconductor component that is caused, for instance, by a short circuit of a load connected in series with the semiconductor component, the current rises far above the rated current. In order to protect the semiconductor component from destruction, the excess current is detected, and the semiconductor component is blocked by an internally generated shutoff signal. A property of field-effect-controlled semiconductor components, that is power MOSFETs and IGBTs (isolated gate bipolar transistors) is that their shutoff time is approximately the same, regardless of the current to be shut off. In other words, the steepness of the shutoff of current upon excess current is substantially greater than in the normal operating situation. As a result, the excess voltages generated upon shutoff at excess current in terms of stray inductance in the load current circuit are substantially higher than upon shutoff at rated load.